Evaluation of Non Chrome Surface Pretreatments

1
Evaluation of Non Chrome Surface Pretreatments
AIR FORCE RESEARCH LABORATORYMATERIALS
MANUFACTURING DIRECTORATE
Dr. Robert Mantz, AFRL/MLBT Dr. Natasha Voevodin,
UDRI Dr. Seva Balbyshev, UTC Dr. Alex Khramov, UTC
2004 Aerospace Coatings Removal and Coatings
Forum 11-12 May 2004
2
Aircraft Coatings
Corrosion Protection Chromate Corrosion
Inhibitors Chromated Surface Treatments
Chromated Primers Survivability
and Signature Reduction Color
Visual Infrared Appearance
Finish, Color, Gloss Abrasion and Chemical
Resistance Weatherability
Topcoat
Primer
A/C Skin
Surface Treatment
3
The Coatings Problem

• Environmental
• gt 70 of AF generated HAZMATS (70-90)
• additional chrome waste reductions could halt
  coating operations
• Costs
• manhours - paint stripping for structure NDI
• hazardous waste disposal
• depot bottleneck
• Durability
• field touch-up
• aircraft unavailability
• VOC generation

• Field Level Touch-Up
• Preparation
• Apply Topcoat

Aircraft Delivery

• Programmed Depot Maintenance
• Strip Topcoat
• Strip Primer
• Cleaning
• Touch-Up
• Apply Primer
• Apply Topcoat
• Spec Marking

• Topcoat Replacement
• Preparation
• Scuff Sand Topcoat
• Cleaning
• Touch-Up Surface Treatment/Primer
• Apply Topcoat

• Field Level Touch-Up
• Preparation
• Apply Topcoat

4
Aging Aircraft Issues

• Weapons systems being used past design life
• Average age all aircraft
• 20 years - 2000
• 30 years by 2015
• Material sustainment needs increasing
• Funding for spares decreasing
• Mission capable rates down 8.8 since Gulf War

Projected service life 80 years
Source Air Force Magazine, November 1998, pg 76
5
Aircraft Coating SystemFunctional Diagram
Research Efforts
Quick Cure APC Topcoat Ultrahydrophobic Coatings
Nonchromate Corrosion Inhibitors
Atmosphere
Top Coat
Primer
Surface Treatment
Substrate
SNAP Surface Treatment
Surface Cleaning / Prep
6
Aircraft Coating SystemFunctional Diagram
Research Efforts
Atmosphere
Top Coat
Primer
Surface Treatment
Substrate
SNAP Surface Treatment
7
Preparation of SNAP Coatings
substrate
GPTMS
TMOS
GPTMSTMOS 31
H2O (H)
hydrolysis (Room Temp)
degreased and deoxidized AA2024-T3 panel
surfactant cross-linker
3 day aging
dip - coating
cured _at_ RT
Crosslinker Polyamine (e.g., DETA)
8
SNAP Sol Gel Introduction

• SNAP process
• hydrolysis and condensation of silanes in aqueous
  solution
• formation of organo-silicate nanoparticles

tetramethoxyorthosilicate (TMOS) and
3-glycidoxypropyltrimethoxysilane (GPTMS)
9
Sol-Gel vs. SNAP

• Sol-Gel chemistry
• Hydrolysis and condensation of metal
• alkoxides

Condensation
Hydrolysis
10
Hydrolysis and CondensationKinetics

• Factors affecting kinetics
• pH
• Acid-catalyzed hydrolysis!
• Relative amount of water
• R value - molar ratio of water to
• hydrolyzable alkoxide

high R
low R
11
SNAP Surface Treatment Coatings
Sol-gel Processing
TMOS
GPTMS
Epoxy-Amine Cure
DETA
12
SNAP Evaluation Coatings Technology Integration
Office
SNAP with Primer Topcoat SNAP Mil-PRF-23377
Mil-PRF-85285C
Standalone SNAP
PASS
PASS
3,000 hours Salt Fog
336 hrs Salt Fog
Filiform Corrosion
13
Chromate Free Coating System Evaluation2000 hour
Salt Spray
SNAPPRC DeSotoAPC
SNAPProduct 1APC
BoegelProduct 1APC
BoegelPRC DeSotoAPC
PreKoteProduct 1APC
PreKotePRC DeSotoAPC
14
Chromate Free Coating Primer Evaluation2000 hour
Salt Spray
SNAPProduct 1
SNAPPRC DeSoto
BoegelProduct 1
BoegelPRC DeSoto
PreKoteProduct 1
PreKotePRC DeSoto
15
Results of GE Impact Test and Tape Adhesion Test
GE Impact gt 10 is passing Tape Test gt 4B is
passing
16
SNAP Crosslinking Agent Variation
Amino-silanes as crosslinkers
Act simultaneously in crosslinking of
nanoparticles and at the coating/substrate
interface improving adhesion and coating
properties
17
Improved Crosslinkers - EIS

• Simultaneously crosslink nanoparticles and
  improve adhesion at the substrate interface.
• Improved barrier properties.

18
Encapsulated Organic Corrosion Inhibitors
 
- Nano-Encapsulation of Corrosion
Inhibitors - Release on Demand / Smart Coating
MBI-CD mercaptobenzimodazole/ß-cyclodextrin
inclusion complex
SVET corrosion current density maps (scribed,
after 24 hr in electrolyte)
Sustained Release and Diminished Corrosion Attack
19
Conclusions

• SNAP Coatings have demonstrated acceptable
  corrosion resistance when used with chromate
  containing primers
• None of the chromate free coating systems has
  demonstrated adequate corrosion protection to
  date
• New chromate free surface treatments and primers
  are being developed
• AFRL/MLBT will continue testing in cooperation
  with CTIO to evaluate chromate free surface
  treatments and primers as they become available.

20
Coatings Research Team

• Funding
• AFOSR
• AFRL/ML